Communication system supporting wireless communication of packet data and method and arrangement relating thereto

ABSTRACT

A communication system supporting communication of packet data. It comprises a core network, which includes a number of packet data support nodes, a number of gateway nodes for communication with external packet data networks, and a number of radio networks. Each radio network includes radio network control means. At least some of the packet data support nodes include a separate functional server node. A number of the functional server nodes are provided to control at least a number of radio network control means such that the functional server nodes are able to control any radio network control means.

BACKGROUND OF THE INVENTION

The present invention relates to wireless communication systemssupporting communication of packet data which include a core network anda number of radio networks, and particularly it relates to the controlof radio networks, e.g. via radio network control means, by packet datasupport nodes of the core network. The invention also relates to apacket data support node in a communication system supportingcommunication of packet data and to a method of controlling, in acommunication system supporting communication of packet data,connections between user stations and/or connections between userstations and external packet data networks.

BRIEF SUMMARY OF THE INVENTION

In communication systems supporting communication of packet dataincluding a number of radio networks and a core network, e.g. a PLMN,each radio network generally comprises radio network control meanscomprising one or more radio network control nodes controlling a numberof base stations to which user stations can be connected or attached.Generally a radio network control means or a radio network control nodeis controlled by a packet data support node of the core network. ForGPRS/UMTS such a packet data support node is denoted an SGSN (ServingGPRS Support Node). Another support node in such a communication systemis the GGSN (Gateway GPRS Support Node) which handles or controlscommunication with external packet data networks. In systems known todaySGSN, or more generally the packet data support node, controls one ormore radio network control means, i.e. it is responsible for such radionetwork control means, for example RNCs. It is fixed which SGSN controlswhich RNC(s).

It has been suggested to split up a packet data support node, orparticularly an SGSN, in two “sub-nodes”, namely an SGSN server andanother sub-node denoted media gateway (MGW) wherein the SGSN servernode handles control plane functionalities and the media gateway handlesuser plane functionalities. However, redundancy issues constitute aproblem in such a system since if an SGSN (or an SGSN server node) ismalfunctioning, another SGSN has to be allocated or a redundant SGSN hasto be provided for. Generally, as a subscriber performs an attachprocedure to the network, the RNC controlling the base station itconnects to, allocates a nearby SGSN (or SGSN server), i.e. which SGSNthat is selected is generally based on the location of the subscriber.

This gives rise to problems also as far as load sharing is concerned,which generally is not handled in any satisfactory manner. As anexample, at rush hours a large number of subscribers move in the samedirection, i.e. towards the center of a town and, since the selection ofSGSN server is location dependent, i.e. it depends on which radionetwork the subscriber has attached to, the SGSN servers in such areasrun the risk of being overloaded whereas other SGSN servers are hardlyused at all. At a later time the situation may be the opposite, i.e. thepreviously hardly loaded SGSNs will be heavily loaded whereas the otherswill have a lot of spare capacity. This means that the SGSNs (or SGSNservers) have to be dimensioned for the “worst case”. Moreover, as asubscriber is roaming within the network such that the closest basestation will be controlled by another radio network control means, thanthe one he attached to, and hence the SGSN which is responsible for aparticular radio network control means is statically configurated, theresponsibility for the connection will be taken over by another SGSN(server) etc. This involves a lot of signalling e.g. with the homelocation node (HLR) of the subscriber, i.e. it requires HLR updateswhich means a load on the HLR and it involves a lot of signalling. Tomake reconfigurations and to add equipment in such a system will alsoinvolve high costs and much complicated configurational work. Stillfurther high costs are involved when such a system needs to be builtout, i.e. when new servers or servers with a greater capacity, orservers replacing malfunctioning servers need to be added. Consequently,the known solutions are disadvantageous as far as load sharing isconcerned and moreover, packet data support node redundancy is notprovided for to a sufficient extent, network configuration work isexpensive, time consuming and complicated. In addition thereto packetdata support nodes are associated with specific radio network controlmeans which means that, for a roaming subscriber, the responsibility forsuch subscriber by a packet data support node will be transferred toother packet data support nodes as the subscriber moves throughout thenetwork. This leads to a lot of signalling between packet data supportnodes and home location nodes of the subscriber in order to updateinvolved nodes (HLR-nodes, SGSN-SGSN, SGSN-GGSN) which puts a high loadon e.g. the home location node and requires a lot of signalling ingeneral. This problem may of course be even more serious from a networkpoint of view if, at a given time, a plurality of subscribers movessubstantially along the same path, cf. rush hour traffic.

SUMMARY OF THE INVENTION

What is needed is therefore a communication system supportingcommunication of packet which system is of a kind that comprises a corenetwork with a number of packet data support nodes (and gateway nodesfor communication with external packet data networks), a number of radionetworks controlled by radio network control means wherein the load onpacket data support nodes can be distributed in an appropriate manner,or in other words is capable of providing for an adequate load sharingamong the packet data support nodes and in which the load of the packetdata support nodes gets as independent of time as possible or at leastdistributed as evenly as possible among the packet data support nodes.

A communication system is also needed in which packet data support noderedundancy can be provided for in an easy and straightforward manner.Still further a system is needed in which configurational work anddevelopment of packet data support nodes can be handled as easily, andefficiently as possible, for example in the case of malfunctioningnodes, introduction of additional equipment or particularly addition ofentire packet data support nodes etc. Further yet a system is needed inwhich operation and maintenance, especially as far as packet datasupport nodes is concerned, can be provided for in a cost efficient,easy and fast manner. Still further a system is needed through which thesignalling relating to controlling packet data support node can bereduced as well as the load on home location nodes for subscribersmoving throughout the network, for example as far as home location nodeupdates relating to such subscribers can be reduced as compared to inhitherto known systems.

Therefore the present invention provides for a communication system asreferred to above in which at least some of the packet data supportnodes are divided into a functional server node (FSN) and a functionaluser gateway node (UGN) Alternatively the functional server nodefunctionality, i.e. the control plane functionalities, of a number ofpacket data support nodes, i.e. functional server nodes, are provided ina pool; no functional user gateway nodes being provided. A number offunctional server nodes are provided to, in common, control at least anumber of routing areas served by different radio network control means.These functional server nodes are arranged to form a pool of functionalserver nodes and each of the functional server nodes in a said pool isable to control any of the radio network control means.

In a particularly advantageous implementation all functional servernodes are included in a pool which is common for the entire network,i.e. all radio networks. Any functional server node may then serve anyradio network control means. Of course there may also be for example twoor more different pools wherein the functional server nodes of a poolcommonly are responsible for a part of the network whereas the remainderof the radio network control means commonly are controlled by thefunctional server nodes of the other pool.

A number of functional server nodes may be located at a first serversite whereas other functional server nodes of the same pool may belocated at a different server site to provide for, in addition tofunctional server redundancy also server site redundancy, thusincreasing the server node redundancy even more. It is of course alsonot necessary to provide one or two sites but the functional servermeans can be arranged in any appropriate manner. It is howeverparticularly advantageous to gather a plurality of functional servernodes at at least one site, or two or more, if redundancy is consideredto an even higher extent.

In a particular implementation the communication system comprises a PLMN(Public LAN Mobile Network) which thus comprises a core network and anumber of radio networks. In an advantageous implementation allfunctional server nodes are able to serve the entire PLMN. A radionetwork control means may particularly comprise one or more radionetwork control nodes for that specific radio network controlling aplurality of base stations. The radio network control nodes communicatewith an allocated or selected functional server node over a controlplane sub-protocol and with the user gateway node over a user planesub-protocol. This means that, to allow the split up of the packet datasupport node, a protocol has to be used which can be divided into acontrol plane sub-protocol and a user plane sub-protocol between thepacket data support node and the radio network. However, also if thereis not such a protocol, the inventive concept may be implemented butthen all communication goes via an UGN which forwards control signallingto the FSN. Such a concept is described in the Provisional U.S. patentapplication Ser. No. 60/152,748 filed on Sep. 9, 1999 by the sameapplicant, and with the title “Method, apparatus and system for enablingcommunication between second generation and third generation packet datanetworks” and the content of which herewith is incorporated herein byreference. This application was followed up by a regular patentapplication based thereon.

Particularly the system comprises GPRS/UMTS and the packet support nodesare SGSN nodes (serving GPRS support nodes) which here are divided intofunctional server nodes (and functional user gateway nodes). The usergateway nodes, if implemented, particularly comprise so called mediagateways (MGW). The radio networks are so called UTRANs and the radionetwork control means of such an UTRAN comprises one or more RNCs. Eachsubscriber or user (equipment) station (UE or US) having initiated anattach procedure to the network is allocated a functional server nodeindependently of the location of the user equipment station, i.e. anyfunctional server node may be selected, and said allocation is alsounaffected by the user station moving throughout the network, if roamingaround in the network. As long as the user is attached or connected, thesame (selected) functional server node may be responsible for thecontrol, of course unless it is subjected to a malfunction or similar.In a particular implementation the allocation of a functional servernode for a subscriber or a user station is maintained at least for agiven time interval or alternatively as long as the subscriber isattached to the network.

In an advantageous implementation a functional server node remainsresponsible for a particular subscriber having been allocated thefunctional server node also when the subscriber has performed a detachprocedure. Information about which was the allocated functional servernode for that particular subscriber may be stored in storing means inthe radio network control means such that when the subscriber againinitiates an attach procedure, the same functional server node may bereused for that subscriber. It is the radio network control means thatare responsible for allocating a functional server node, or for aselecting a functional server node, for a subscriber performing anattach procedure to get attached to the network.

A radio network control means may allocate or select a functional servernode in different ways. In one implementation consecutive subscriberswhich are attaching/connecting to the network over a particular radionetwork control node, are allocated different functional server nodeswhich means that the radio network control means selects differentfunctional server nodes for consecutively connecting or attachingsubscribers. This can also be done in different manners, consecutivesubscribers can be allocated different functional server means accordingto any given scheme or in any given order. It is also possible torandomly select a functional server means for each subscriber. Then mayof course two consecutive subscribers be allocated the same functionalserver node; however, this is not important since in principle it is notnecessary that consecutive subscribers actually are allocated differentfunctional server means. In an alternative implementation subscribersgroupwise are allocated functional server means such that for examplefive subscribers may be allocated a first functional server means, thenext group of subscribers may be allocated another functional servermeans etc. This is not a critical issue, the main thing being that theselection or allocation of functional server means remains at least aslong as the subscriber is attached, i.e. that it is not dependent on thelocation of a radio network control means but that the load from eachradio network control means can be evened out among the functionalserver means such that a good load sharing is provided as well asredundancy. It is an efficient means to handle an uneven load in thenetwork, cf. the situation initially referred to when a lot ofsubscribers at the same time move in the same direction etc. or when alarge amount of subscribers at the same time are at the same place etc.

In a particular implementation each functional server node includes afunctionality for selecting functional user gateway node for eachsubscriber for which the particular functional server node has beenselected. The functional server node may select an optional functionaluser gateway node for a subscriber or, alternatively, a functionalserver node has to select a user gateway node that is close to thesubscriber, or according to a given scheme or algorithm. Also this canbe done in any appropriate manner. Further still, advantageously thefunctional server node is responsible for selecting packet data gatewaysupport node for communication with external packet data networks. Thiscan also be done in different manners.

The invention also provides for a packet data support node for mobilityand session management in a communication system supportingcommunication of packet data. The packet data support node is dividedinto a functional server node and a user gateway node, or comprises atleast a (separate) functional server node. The functional server nodeforms part of a pool of functional server nodes and, in common with saidother functional server nodes, it is able to serve at least a given partof the communication system, i.e. at least a number of routing areas ora number of radio networks, particularly radio network control meanscontrolling a number of different radio networks. This means that saidfunctional server node is responsible for all radio network controlmeans within the given part of the network.

In one implementation all functional server nodes in the pool areresponsible for the entire network which means that the functionalserver node itself shares the responsibility for all radio networkcontrol means with all other functional server nodes and that it can beselected or allocated by any of the radio network control means. Thefunctional server node particularly comprises means for selecting a usergateway node for a subscriber (connection) to which it has beenallocated as a functional server node or, in other words, for which ithas been selected by the radio network control means controlling thebase station serving the subscriber or the user station of thesubscriber.

The action of selecting a user gateway node can be performed indifferent ways. In one implementation a user gateway node can beselected freely. In an alternative embodiment the selection can be doneaccording to some given requirements. In a particular embodiment theuser gateway node closest to the subscriber having initiated an attachprocedure should be “selected”; other criterias are however alsoapplicable and any such selection model is intended to be covered by thescope of the present invention. In a particular implementation thepacket data support node is an SGSN of the GPRS/UTMS system which isdivided into a functional server node (SGSN server) and a user gatewaynode wherein the user gateway node comprises a so called media gateway.Particularly the functional server node is responsible for the selectionof a user gateway node or a MGW. In one implementation the selection canbe done mor or less freely and in an alternative implementation the MGWclosest to the radio network control means should be “selected”. Alsoother selection procedures are possible.

The invention therefore also discloses a method, in a communicationsystem, comprising a core network and a number of radio networks, andwhich supports communication of packet data, for controlling connectionsbetween user (equipment) stations and/or between user (equipment)stations and external packet data networks, wherein user stations areconnected to radio networks each of which is controlled by a radionetwork control means and wherein packet data support nodes are providedfor radio network control. According to the invention a packet datasupport node is divided into a functional server node and a user gatewaynode for control plane applications and user plane applicationsrespectively. The method includes the steps of; providing a pool offunctional server nodes; commonly controlling at least a part of thenetwork by said functional server nodes such that any functional servernode in the pool may control any connection irrespectively of in whichradio network the user station is located.

In a particular implementation the method includes the steps of;selecting, arbitrarily or according to a given scheme, a functionalserver node for a subscriber having initiated an attach procedure to thenetwork; maintaining said functional server node for said subscriber/theuser station irrespectively of where in the network the subscriber is.Advantageously the method includes the steps of; selecting differentfunctional server nodes for consecutive subscribers performing a networkattach procedure over a particular radio network. The selection offunctional server node is performed by the radio network control meanscontrolling the radio network to which a subscriber attaches. The methodparticularly also includes the steps of; selecting a user gateway nodefrom the allocated or selected functional server node; selecting agateway support node for access to external packet data networks alsofrom the allocated functional server node.

Thus, in an advantageous implementation, when a functional server hasbeen selected and a subscriber has performed an attach procedure andduring a PDP-context request procedure the functional server nodeselects a user gateway node which also can be done in any manner but inan advantageous implementation a user gateway node close to the radionetwork control means, i.e. to the subscriber, is selected.

The functional server node also is responsible of selecting a gatewaysupport node for access to external packet data networks. Generally eachradio network control means contains information about which are thefunctional server nodes and, for example, for each subsequent subscriberconnecting to the network, a different functional server means isselected e.g. according to a rolling scheme, this may however be done inmany different ways and the main point is that not all subscribersconnecting or attaching via a particular radio network control means areallocated the same functional server node and moreover that a functionalserver node is kept even if the subscriber moves throughout the networkand hence the signalling load is reduced and it is avoided that the homelocation node or HLR of the subscriber continuously has to be updated.In one embodiment, storing means are provided in the radio networkcontrol means for, at least for a given time period, storing informationabout which was the most recently selected functional server node for aparticular subscriber who has become detached from the network such thatupon reattachment to the network, the same functional server node mayagain be selected for that subscriber.

In different implementations the control plane functionality of a packetdata support node is provided in one or more pools as discussed aboveand no user gateways for user plane functionalities are implemented butthere is a direct tunnel from radio network control means to a packetdata gateway support node (e.g. GGSN).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be further described in anon-limiting manner and with reference to the accompanying drawings, inwhich:

FIG. 1 schematically illustrates a communication system with a pool offunctional server means,

FIG. 2 is a figure similar to that of FIG. 1 wherein a communicationsystem comprising GPRS/UMTS comprises a number of functional servernodes consisting of SGSN server nodes and user gateway nodes comprisingmedia gateways,

FIG. 3 illustrates an alternative implementation with two pools withfunctional server means,

FIG. 4A schematically illustrates the attach procedure in sequentialsteps,

FIG. 4B schematically illustrates the PDP Context activation procedurein sequential steps,

FIG. 5A is a flow diagram schematically illustrating one way to select afunctional server node from a radio network control means and the attachprocedure,

FIG. 5B illustrates a PDP Context activation procedure,

FIG. 6 is a schematical flow diagram illustrating the selection of auser gateway node from a functional server means, and

FIG. 7 is a flow diagram schematically illustrating selection of gatewaysupport node, GGSN, by the functional server node, SGSN server node.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows one way of implementing the inventive concept. Acommunication system supporting communication of packet data isdisclosed. It comprises an IP connectivity backbone network and a numberof radio networks RAN1, RAN2, . . . , RAN6 (of which only RAN1-RAN3 areexplicitly indicated in the Figure). Each radio network comprises anumber of base stations BS which are controlled by radio network controlmeans RNC 11, . . . , RNC 16 respectively. In the figure user equipmentstation UE_(A) is illustrated which e.g. comprises a computer connectedto a mobile station MS_(A) which here connects to RAN2. Packet datasupport node functionality is provided by functional server nodes FSNand user gateway nodes UGN respectively. Thus, a number of decomposedpacket data support nodes are provided as FSN 1-FSN 8 and UGN 21-26.

The functional server nodes FSN 1, . . . , FSN 8 are provided in a pool100 and they share the responsibility for the control of, here, all theradio networks RAN1, . . . , RAN6 meaning that any FSN of the pool isable control any of the radio networks. In this embodiment thefunctional server nodes are provided at two different sites, site 10 andsite 20 respectively, for redundancy reasons, which is clearlyadvantageous for example if one site for one reason or another isdestroyed for example due to fire or sabotage. Of course there may bemore than two sites and it is of course also possible to keep all thefunctional server means at a single site as well. Other alternatives arealso possible. Thus, in this embodiment FSN 1, . . . , FSN 4 areprovided at site 10 whereas FSN 5, . . . , FSN 8 are provided at site20. It should be noted that in this case all the functional server nodesare provided in a common pool. It is also possible to have more than onepool depending for example on geographical and practical considerations.FSN 1, . . . , FSN 4 are connected to router R5 which in turn isconnected to router R1 of the backbone network which is in direct orindirect communication with the other routers of the backbone, hereR2,R3,R4. In a similar manner FSN 5, . . . , FSN 8 are connected torouter R6 at site 20 which in turn communicates directly with router R4of the backbone network. The routers on the links of the backbonenetwork as well as routers at the respective sites may be arranged inany appropriate manner. It is also possible to provide for redundantrouters and links in the backbone network.

Packet data gateway support nodes GW1,GW2,GW3 are provided forconnection to external packet data networks such as Internet, intranetsand corporate LANs. The connection to an external network can be donethrough one or more GW:s. If there are more than one gateway to anexternal network a selection of gateways is needed at each connectionactivation. The home location register HLR and domain name server DNSare connected to connectivity backbone via router R4, but they can ofcourse be connected in any other appropriate manner.

The radio network control means RNC 11, . . . , 16 are responsible forselecting a functional server node when a subscriber connects/attachesto the network. Thus, when user equipment UE_(A) initiates an attach orconnect procedure to be attached to the network via a base station ofRAN2, RNC 12, which controls RAN2, is responsible for selecting afunctional server node FSN. In principle RNC 12 may select any of theFSNs of pool 100 to control the subscriber of user equipment UE_(A). Itis here supposed that RNC 12 selects FSN 3. Advantageously the selectionof FSN is done taking load sharing, FSN status etc into consideration.The selection can be performed in different ways, for example a WeightedRound-Robin WRR selection method with reject possibility may be used.This generally means that for each connection or attachment, another orthe subsequent FSN is selected, i.e. for the next connecting subscriber,RNC 12 would select for example FSN 4. A weighting factor in a WRRselection method may be a factor which takes the capacity (configuredcapacity) of each FSN server into account. The actual load on the FSNcan also be included in the weighing factor as other factors as well. AnFSN server may be provided with the possibility of rejecting a requestby an RNC and then the RNC will try another FSN server node. In anadvantageous implementation the selection method also includes thepossibility to return information in a reject message, e.g. the causefor the rejection, the current load status of the concerned functionalserver node etc. Advantageously each RNC keeps information about thestatus of the different FSN servers and inputs this to the selectionalgorithm.

In a particularly advantageous implementation an RNC keeps informationabout which FSN server a user equipment station has previously used.This information can then with advantage be used when a detached userreattaches and the FSN be reused. In that manner signalling is reducedor minimized and there is no need to get information about the oldcontext in the old FSN server. It may also be used if the bearer on theused communication protocol has been temporarily released and then it isneeded when the bearer is to be setup again. However, the informationstored in an RNC is only kept for a given time period, otherwise thestoring capacity would have to be unnecessarily high and too oldinformation is generally not useful.

In one embodiment statistics relating to the number of rejects orreasons for rejections etc. by different FSN's is kept in the RNC:s. Itis also possible to keep such information in an FSN or in both RNC andFSN. The information can be used to indicate which is the capacity andto trigger a capacity increase. Which FSN is allocated or selected for aparticular subscriber or user station, is independent of where in thenetwork the subscriber is, and no change of FSN is needed if thesubscriber or user station moves to other routing areas or radionetworks but the same FSN server may be kept. This means that nointer-functional server node Router Area update is needed which in turnwill have as a consequence that less signalling than in hitherto knownsystems is needed and no HLR updates are required for such purposes. Theby FSN temporarily assigned user station (UE) identity (P-TMSI) (whichis stored in the user station at detach and power off) can be used tofind the previously used FSN in case a user has moved to another RNC.Different ways to code FSN into user station identity can be used, e.g.by some bits identifying FSN etc.

Since all FSN servers have substantially the same or identicalconfiguration, the operation and maintenance costs will be low, muchlower than in hitherto known systems and it also makes it easier to addmore capacity e.g. through adding a new FSN. The parameter and softwareconfigurations of the FSN:s are advantageously more or less identical.The hardware configuration may of course be different, capacity maydiffer etc.

If there are more than one pool serving the network, then all FSN:swithin a pool particularly have identical parameter and SWconfiguration. Since there are always alternative FSN:s that can be usedif a complete node fails, redundancy on network level is obtained andthe redundancy requirements on the FSN will not be as stringent as therequirements on server nodes/packet data support nodes in hitherto knownsystems. When the packet data support nodes are divided into twofunctional nodes, the functional server nodes generally handle thecontrol plane functionalities whereas the user gateway nodes handle theuser plane functionalities. This will be further described withreference to FIG. 2 below which is a figure similar to that of FIG. 1but specifically showing an UMTS-implementation.

In an advantageous embodiment, when an RNC has selected a functionalserver node FSN for a user station or a subscriber attaching to thenetwork, the allocated or selected FSN is responsible for selection of auser gateway node. Particularly each FSN server within a pool cancommunicate with any user gateway node UGN in the network (or the partcontrolled by the pool), and each user gateway node UGN can be used byany functional server node FSN in the network of the pool. According toone implementation the FSN “selects” the UGN connected to the RNC itcommunicates with; i.e. by which it was selected. (Then there is a 1:Mrelationship between user gateway node UGN and radio network controlmeans RNC.)

In an alternative implementation FSN selects UGN in a more free manner.In one implementation an algorithm is used according to which thenearest UGN is tried first. Then there is a M:N relationship between UGNand RNC. This is advantageous in so far that it also provides for UGNredundancy. Particularly the UGN closest to the concerned RNC should beselected first to minimize backbone capacity usage and if this UGN isnot available or if it rejects the request, another UGN is selected. Inone particular implementation, in case of a reject, a weightedRound-Robin algorithm may be used to select an alternative UGN. If UGNis selected without restrictions, at least to some extent, or if morethan one UGN is selectable, this provides for redundancy on a networklevel as far as functional user gateway nodes are concerned and therewill always be alternative UGN that can be used if a complete UGN fails.The redundancy requirements on such nodes will also be less stringent.It is also advantageous in that upgrading operations are facilitatede.g. when one UGN node is taken out of traffic. Still further, in oneimplementation it could be an option to use the same UGN untildeactivation or detachment.

Still further, in one implementation the selected functional server nodeis responsible for selecting between several gateway nodes to externalpacket data networks such as for example Internet or an intranet formulti-homed APNs (Access Point Name). According to different embodimentsthe nearest gateway node is selected first or alternatively somealgorithm is used such as the already mentioned weighted Round-Robinalgorithm. In one particular implementation load and/or capacityconsiderations are included in the algorithm. Thus it can be providedfor redundancy on network level also as far as gateway node to externalnetwork is concerned. There will always be alternative nodes to use if acomplete gateway node fails and redundancy requirements will be lessstringent on such nodes than in known systems. It will also for suchnodes be easy to upgrade them e.g. by taking nodes out of traffic etc.

FIG. 2 shows an implementation of the inventive concept to UTMS. Packetdata support nodes here comprise SGSNs (Serving GPRS Support Node) andthey are divided or decomposed into an SGSN server node and a mediagateway (MGW). In other aspects this figure is similar to FIG. 1 andSGSN server nodes 1 ₁, . . . , 8 ₁ are located at two different sites 10₁,20 ₁ and all form part of a common pool 100. However, in this figuremedia gateway 23 ₁ is connected to router R9 which is in connection withRNC 13 ₁ of the radio network and with router R2 of the IP backbonenetwork. In this way redundant MGWs are implemented. A correspondingrouter can be connected to the other MGWs as well (cf. FIG. 3). Theconcept of providing redundant user gateway nodes was more thoroughlydescribed above but here the specifically implementation of an UGN inthe form of a media gateway MGW is shown. For concepts, terminology etc.that is used it is referred to 3GTS 23.060 v3.4.0 (2000-07), TechnicalSpecification by 3^(rd) Generation Partnership Project (3GPP™) whichherewith is incorporated herein by reference.

In the following the decomposition or splitting up of an SGSN node intoan SGSN server and a media gateway MGW will be more thoroughlyexplained. An SGSN normally handles a large part of user and controlplane functions. When split up, the SGSN server node will handle all thesignalling interfaces (Gs,Gr,Gd etc.) as well as the GTP-C protocolwhereas the MGW will handle the user traffic, and in particular theGTP-U protocol. Thus the load, in the state of the art, supported by theSGSN, will be distributed over two different network elements, SGSNserver node and MGW. A new interface is introduced between SGSN servernode and MGW, however, this will require some additional processing andsignalling but this will be quite insignificant and almost entirelyoffset by the general advantages provided for through the split-up. In aparticular implementation the functions of the SGSN server node will besession management, mobility management, GTP-C termination, MAPtermination, RANAP termination, CDR handling, media gateway selection,GGSN-selection, provision of intercept related information. Theprotocols referred to above, GTP-C, GTP Control Plane, GTP meaning GPRSTunneling Protocol, MAP, RANAP (Radio Access Network ApplicationProtocol) are discussed in 3GPP, 3G TS 23.060 v3.4.0 (2000-07).

The media gateway node will include the functionalities of GTP-U (GTPUser Plane) termination, collection of usage information for chargingand network surveillance purposes, reporting of usage information ondemand or event to the SGSN server node or other nodes, provision ofcontent of communication etc.

The SGSN server node may control the MGW through the Mc interfacefollowing the ITU-T H.248/IETF MEGACO Standard and GGSN through the Gninterface by means of GTP-C messages. GTP-U packets are transferredbetween the MGW and the GGSN over the Gn interface and between the MGWand RNC over the Iu interface following the GTP-U specification, cf. the3GPP document referred to above. Through splitting up an SGSN into anSGSN server node and an MGW, there will only be a functional impact onthe SGSN itself and RNCs, GGSNs and other SGSNs as well as the protocolsthat are used between these nodes are not affected by the decomposition.Besides the Mc interface between the SGSN server and MGW, no otherinterfaces are impacted. The SGSN server node is a main control node forUMTS (and GPRS). It handles all the signalling interfaces of a 3GPPrelease 1999 SGSN including the GTP-C protocol on the Gn and Gpinterfaces and the RANAP protocol on the Iu interface. The SGSN servercontrols the media gateway through the Mc interface following the H.248Standard. The SGSN server supports the Iu interface for UMTS and, in oneimplementation, the Gb interface for GPRS for GSM.

The MGW handles the user plane functionality for GPRS and terminates theGTP-U tunnels towards the GGSN over the G_(N) and G_(P) interfaces andtowards the RNC over the Iu interface. The MGW is controlled by the SGSNserver through the Mc interface following the H.248 standard. For UMTSthe MGW is controlled by the SGSN server through the Mc interfacesupporting the H.248 protocol with the GRPS specific extensions, the Iuinterface between the RNC and the SGSN server supports the RANAPprotocol. Mc and RANAP belong to the control plane as well as the Iuinterface between the RNC and MGW which supports the GTP-U protocol. InUMTS the Gn interface between the SGSN server node and the GGSN supportsthe GTP-C protocol and belongs to the control plane. As referred toearlier, the protocols and the terminology can be found in 3GPP, 3G TS23.060 which was incorporated herein by reference thereto.

The inventive concept also covers an implementation in which FSN:s (SGSNservers) are provided in one or more pools but in which there are noUGN:s, i.e. no nodes or means handling user plane functionalities whichmight not be necessary for packet switched data. For circuit switchedtraffic, such nodes are however generally needed, RNC:s then communicatedirectly with FSN:s.

FIG. 3 shows an alternative implementation of the inventive concept. Itis here discussed with reference to UMTS, but it should be clear that itis generally applicable to any system and particularly any systemwherein the protocol between the radio network and the packet datasupport node can be divided between control plan functionalities anduser plan functionalities.

SGSN server nodes are provided in two different pools, pool A 100 andpool B 200 respectively. The functional server nodes, particularly SGSNserver nodes 1A,2A,3A of pool A 100 are located at site 10 _(AB) whereasfunctional server nodes 4A,5A,6A of pool A 100 are located at site 20_(AB). Correspondingly functional server nodes 1B,2B,3B of pool B 200are located at site 10 _(AB) whereas functional server nodes 4B,5B,6B ofpool B 200 are located at site 20 _(AB). Functional server means of oneand the same pool are located at different sites for reasons ofredundancy in case a site is destroyed due to sabotage, fire, or is outof operation for some other reason, RNCs 11 ₂,12 ₂,13 ₂ are herecontrolled by pool A whereas RNCs 14 ₂,15 ₂,16 ₂ are controlled by poolB. In this embodiment all media gateways 21 ₂,22 ₂,23 ₂, 24 ₂, 25 ₂,26 ₂are connected to routers R7,R8,R9,R10,R11,R12 respectively enabling theuse of redundant media gateways as also discussed with reference to FIG.2. It should be noted that MGW 25 ₂ is connected both to RNC 15 ₂ and toR11, which is an alternative that also could be represented elsewhere,of course R11 might be connected as e.g R10. In other aspects the figureis similar to those of FIG. 1, FIG. 2.

It is possible to, instead of one pool at two sites (here FIG. 1, FIG.2), or two pools sharing two sites, have one pool at one site only;however then redundancy is not as good, or two pools at only one site,three pools sharing two sites or three sites or any other convenientconstellation. In a particular implementation two or more sites areco-located but still separate. Alternatively two sites may have entirelydifferent locations.

It is common for all embodiments that the number of FSN:s (SGSN servers)can be changed arbitrarily without affecting the network structure.Particularly if the number of subscribers increases, simply more FSN:s(SGSN servers) are added—there is no need to add UGN:s (MGW:s), RNC:s,BS:s etc which is extremely advantageous.

FIG. 4A shows an example on attach procedure when the inventive conceptis implemented. An attach request is sent from US1 to RNC on the RLC(Radio Link Control) protocol. I indicates the SGSN server selectionprocedure as further described e.g. with reference to FIG. 5A. When aSGSN server has been selected, the attach request is sent on to SGSNserver using the RANAP protocol. Thereon follows an authenticationprocedure, e.g. in a conventional manner (cf. 3G TS 23.060 V.3.4.0(2000-07). Subsequently steps relating to location updating includinginsertion of subscriber data and finally an Update LocationAcknowledgement is sent to the selected SGSN server. After this step anew P-TMSI (Packet TMSI) is allocated, illustrated by II in the Figure.Then follows an Attach Accept from SGSN server to RNC on the RANAPprotocol. At reception of Attach Accept in RNC, information about thenew P-TMSI and selected (and accepting) SGSN server is stored in RNC(III). Finally an Attach Accept is sent to US1 using the RLC-protocol.

FIG. 4B illustrates an example on PDP Context Activation procedure whenthe SGSN pool server concept according to the invention is implemented.An Activate PDP Context Request is sent from US1 to RNC using the RLCprotocol. At that stage, cf. IV in FIG. 4B, an SGSN server lookup isperformed. This is further described in FIG. 5B below. If there isinformation about which is the selected (and accepting) SGSN server, theActivate PDP Context Request is sent on to the selected (looked up) SGSNserver using RANAP. Then a MGW selection is performed, this is furtherdescribed with reference to FIG. 6. SGSN server then sends an AddContext for Iu tunnel end-point to MGW, which returns Reply Add Contextwith Iu tunnel end-point to SGSN server.

Then follows RAB (Radio Access Bearer) Request from SGSN server to RNC,and corresponding response. Subsequently SGSN sends a modify Context Iutunnel end point and add Context for Gn tunnel end point request to MGW,which returns a response to SGSN server. Thereafter SGSN server sends aDNS query to DNS (Domain Name Server), and following on the response, aGGSN may be selected, VI. How this can be done is further discussed inFIG. 7 below. Subsequently a Create PDP Context Request is sent to theselected GGSN which returns a response to SGSN server. A Modify Contextmessage (with Gn tunnel end-point) is sent to MGW, which confirms toSGSN server. Finally an Activate PDP Context Accept is sent from SGSNserver to RNC using RANAP. An activate PDP Context Accept is forwardedfrom RNC to US1 using the RLC-protocol.

The order in which tunnel end points are added and modified in MGW canbe different.

In the flow diagram of FIG. 5A the selection of an SGSN server node asinitiated by an attach request is described, particularly relating tothe UMTS system and according to one implementation. First it issupposed that an attach request from a user station, here denoted US1,is received in RNC X, 101. RNC X checks in storing means if there is anyinformation about a recently used SGSN server node for US1, generallythe most recently used SGSN server, 102. If the storing means containssuch information, the attach request is sent on by RNC X to the previousSGSN server node, 103. It is then established if the “previous” SGSNserver accepts the attach request, 104. If not, a reject message is sentto RNC X, 105. In a preferred implementation the message containsinformation about why the request is rejected and about the status ofthe “previous” SGSN server. In an alternative implementation the SYSNserver stored as “previous” SYSN server does not have to be used, butother SYSN servers can be used, e.g. to take load situation intoaccount, even if then more signalling is needed. If a reject is receivedfrom SGSN server, then RNC X selects a SGSN server from the poolresponsible for RNC X, e.g. using an algorithm, such as WRR taking SGSNserver status and possible rejects into consideration, 106. An attachrequest is then sent to the selected SGSN server, 107. If the attachrequest is not accepted, the selected SGSN server sends a rejectmessage, preferably with information about the reason for the rejectionand about status, to RNC X, 109, similar to step 105 discussed above. Anew SGSN server is then selected, and the procedure is repeated as fromstep 106 and onwards, preferably until the attach request is accepted.

The intelligence for making such decisions may reside in SGSN serverusing a reject mechanism to trigger the selection of a new SYSN server.

The sending of reject messages need not be compulsory; in an alternativeimplementation a new SGSN server is selected unless an acceptance isreceived, or if the selection is completed (attach request confirmed)within a predetermined time interval. Various alternatives are possiblefor settling that a selection was not successful. If, on the other hand,the selected SGSN server node accepts being selected, theselection/allocation is completed, 110, and an accept message isforwarded to RNC X, 110. The information on selected/allocated SGSNserver is then stored in RNC, 111. From RNC the accept message isforwarded to US1, 112, and then the selection and attach procedures arecompleted, 113.

FIG. 5B illustrates the reception in RNC X of a PDP Context Activationrequest from US1, 114. (The PDP Context Activation procedure isdescribed in 3GPP TS 23.060 as referred to earlier in this document.) Itis examined if there is any information on selected/allocated SGSNserver for US1 in the storing means of RNC X, 115. If not, an errormessage is returned to US1, 116. The reason will presumably that noattach procedure has been done/completed. If information is contained inthe RNC X storing means, the activate PDP Context Request from US1 issent on to the selected SGSN server by RNC X, 117. After a signallingprocedure e.g. as disclosed in the above mentioned document,(illustrated through a dashed line), the PDP Context Activation requestis accepted, 118.

During the procedure of activating a PDP Context Request, a MGW isselected by the SGSN server node. If no MGW:s are implemented, a tunnelmay instead be set-up directly to the appropriate GGSN. Finally packetscan be routed between US1 and GGSN, 119.

FIG. 6 illustrates the procedure of selecting MGW, which preferably isthe responsibility of the selected SGSN server (on condition that MGWsare actually implemented), 201. The selection takes place between steps117, 118 of FIG. 5B.

A step, 202, may be included to establish if there actually areredundant MGWs. If not, the MGW which is connected to the RNC havingselected the SGSN server is “selected”, 203. If, however, redundant MGWsare implemented, a request is sent from the selected SGSN server to theMGW_(i), that is closest to the RNC having selected the SGSN server,204. Subsequently it is established if the selection is accepted byMGW_(i), 205. If yes, MGW_(i) is selected and used for user planefunctionalities. If on the other hand MGW_(i) does not accept theselection, the SGSN server selects the next MGW_(i), i=i+1 according toa scheme or an algorithm, e.g. WRR as discussed with respect to SGSNserver selection. Reject messages with or without accompanyinginformation may be sent from MGW_(i) to SGSN server. Also sending ofaccept messages may be implemented. A new request is then sent to thesubsequent MGW_(i), wherein i=i+1, 208. The procedure is particularlyrepeated from step 205 until a MGW_(i) is found that accepts beingselected.

FIG. 7 relates to selection of GGSN according to a particular embodimentin which the selected SGSN server is responsible for selection of GGSN,301. A request is sent from SGSN server to DNS (Domain Name Server) toget a list of GGSNs for the requested external network/APN, 302.Subsequently it is checked if there are more than one SGSN on thereturned list, 303. If not, a create PDP Context Request is sent to the“selected” GGSN, 308. It is then examined if GGSN accepts the request,309. If yes, the routing setup between US1 and GGSN is finished, orcompleted, 310, and an activate PDP Context accept is returned to US1.Otherwise a PDP Context Reject is returned to US1, 311. If it, on theother hand, is established that there are more than one GGSN:s on thelist, a GGSN is selected from the list taking into consideration GGSNcapacity, GGSN load situation, GGSN location compared to used MGW andRNC, earlier selected GGSN etc., 304. When a GGSN thus has beenselected, a create PDP Context Request is sent to it, 305. It isexamined whether the request is accepted or not, 306. If yes, therouting setup between US1 and GGSN is finished, 310, and then anactivate PDP Context accept is returned to US1. If not, it is checked ifthere is any GGSN left on the list, 307. If not, a PDP Context Reject isreturned to US1, 311. If there still is one (or more) GGSN(s) left onthe list, is returned to step 304, etc.

It should be clear that the invention is not limited to the illustratedembodiment but it may be varied in a number of way within the scope ofthe appended claims, particularly FSNs may be provided in one or morepools (at one or more sites), UGNs may be implemented or not (for packetbased communication). If UGNs (MGWs) are used, they may be selected inany conventional manner, or according to the procedures as discussedherein. The selection of SGSN may also be done in a conventional manner,or as disclosed herein. Particularly, as an alternative, selection ofSGSN server (FSN) may be completed before any attach request isforwarded from RNC through separate signalling, and not until an accepthas been received by RNC (or e.g. when a time interval has expired) theattach request is sent on to the selected FSN (SGSN server) havingaccepted being selected.

1. A communication system supporting communication of packet data withina packet data network, comprising: a core network further comprising aplurality of packet data support nodes; and a plurality of gateway nodesfor communicating with external packet data networks; a plurality ofradio networks wherein each radio network includes means for controllingsaid each radio network; wherein some of said plurality of packet datasupport nodes further comprises a plurality of functional server nodesforming a common pool and wherein each of said functional server nodeswithin said common pool is able to be associated with and control any ofsaid means for controlling said each radio network; and wherein each ofsaid means for controlling radio networks further comprises means forperforming an attach procedure to attach a particular user station to aparticular one of said plurality of functional server nodes independentof the location of said user station and unaffected by the roaming ofsaid user station.
 2. The communication system of claim 1 wherein saidplurality of function server nodes are formed into two or more commonpools wherein each common pool controls an assigned part of said packetdata network and wherein each function server node within a particularpool is able to be associated with and control any of said means forcontrolling said each radio network within said assigned part of saidpacket data network.
 3. The communication system of claim 1 wherein saidpacket data network comprises a public land mobile network (PLMN) andsaid common pool of function server nodes are able to serve said entirePLMN.
 4. The communication system of claim 1 wherein said means forcontrolling said each radio network includes a radio network control(RNC) node communicating with a functional server node over a controlplane subprotocol.
 5. The communication system of claim 1 comprises aGeneral Packet Radio Service (GPRS) wherein said functional server nodesare Serving GPRS Support Node (SGSN) and wherein said GPRS comprisesmedia gateway nodes (MGW).
 6. The communication system of claim 1wherein said means for performing said attachment selects a particularone of said functional server node within said common pool to evenlydistribute the capacity within said common pool.
 7. The communicationsystem of claim 1 wherein the attachment of said user station to saidparticular function server node is maintained at least for a given timeperiod.
 8. The communication system of claim 1 wherein said means forperforming said attach procedure further comprises a record for storinginformation about which particular user station is attached to whichfunctional server node such that in the event said user station isdetached from said functional server node and then re-attempts to attachto said communication system, said means for performing said attachprocedure re-attaches said user station with said same functional servernode as indicated by said record.
 9. The communication system of claim 8wherein said user station is re-attached to said function server noderegardless of which radio network control means is now serving said userstation.
 10. The communication system of claim 1 wherein each of saidfunctional server nodes further comprises means for accepting orrejecting an attach attempt associated with said attach procedureperformed by a particular means for controlling said radio network. 11.The communication system of claim 1 wherein said plurality of packetdata support nodes further comprise a plurality of user gateway nodesand wherein each of said functional server node comprises means forselecting a particular one of said plurality of user gateway nodes foreach user station attached to said each functional server node.
 12. Thecommunication system of claim 1 wherein each of said functional servernode selects a user gateway node closest to a radio network serving aparticular user station.
 13. A method of providing communication withina communication system including a core network and a number of radionetworks providing radio connection to a plurality of user stations,wherein said core network further includes packet data support nodes,comprising the steps of: providing a plurality of functional servernodes within said packet data support nodes into a common pool;receiving a request from a particular user station to attach to saidcommunication system by a particular radio network serving said userstation; and selecting, by said radio network, a particular one of saidplurality of functional server node irrespective of said locationassociated with said user station or said radio network such that evendistribution of overall network capacity can be performed within saidplurality of functional server nodes for said plurality of user stationsbeing served by said communication system, wherein the step of selectinga particular one of said plurality of functional server node includesperforming an attach procedure to attach a particular user station to aparticular one of said plurality of functional server nodes independentof the location of said user station and unaffected by the roaming ofsaid user station.
 14. The method of claim 13 wherein said step ofselecting selects a different functional server node for consecutiveuser stations performing a network attach procedure.
 15. The method ofclaim 13 wherein said packet data support nodes further include aplurality of user gateway nodes, further comprising the step of saidfunctional server node selected for a particular user station furtherselecting a particular one from said plurality of user gateway nodes.16. The method of claim 13 wherein said communication network furtherincludes a plurality of gateway support node, further comprising thestep of said functional server node selected for a particular userstation further selecting a particular one of said plurality of gatewaysupport nodes for communicating with an external packet data network.17. The method of claim 13 wherein in the event a particular userstation is attached to a particular functional server node and then hasbeen de-attached from said communication network, further comprising thesteps of: receiving a request from said user station to attach to saidcommunication network; identifying said functional server nodepreviously attached to said user station; and re-attaching said userstation to said same functional server node.
 18. A packet datacommunication system including a core network and a plurality of radionetworks associated with said core network wherein said core networkfurther includes a plurality of functional server nodes and wherein saidplurality of radio networks provides radio coverage to a plurality ofuser stations within a particular network coverage area, comprising:means for receiving a request from a particular one of said userstations to attach to said packet data communication system; and meansfor selecting a particular one of said functional server nodes to beattached to said user station wherein said means for selecting is ableto select any one of said functional server nodes without consideringthe location of said user station or the location of said means forselecting within said packet data communication system and wherein noone particular functional server node is pre-assigned to said means forselecting; wherein said means for selecting a particular one of saidfunctional server nodes includes means for performing an attachprocedure to attach a particular user station to a particular one ofsaid plurality of functional server nodes independent of the location ofsaid user station and unaffected by the roaming of said user station.19. The packet data communication system of claim 18 further comprisingmeans for storing the identity of a particular functional server nodeattached to said user station and in the event said user station isde-attached and then attempts to re-attach to said packet datacommunications system, said means for selecting selects said samefunctional server node previously attached to said user station byaccessing said means for storing.
 20. The packet data communicationsystem of claim 18 wherein said means for selecting selects particularones of said functional server nodes to evenly distribute the capacityassociated with handling data communicated with said plurality of userstations within said packet data communication system.